Considerable amounts of ecotoxicological data have been generated since the discovery of perchlorate contamination in the environment to assist in evaluating the potential for ecological exposures and subsequent effects. This chapter attempts to provide a synopsis of, and to interpret the available ecological data pertaining to perchlorate, and to identify areas in need of further study. Perchlorate is an oxidizing anion found as a contaminant in ground and surface waters as a result of the dissolution of perchlorate salts (ammonium, potassium, magnesium, and sodium). Perchlorate salts are highly watersoluble and, in aqueous solution, perchlorate is quite unreactive within the range of temperatures and pHs normally encountered in the environment. 1 Once in water, perchlorate can persist for many years, and water serves as a carrier. Because it is an anion, perchlorate does not adsorb to soils and its adsorption to minerals is weak and reversible.2.